ME PhD Oral Examination: Young Beom Kim (Friday, May 13th, 10:00am)

                                                                                             Stanford University Ph.D. Dissertation Defense 


                                                                      Title: "Nanoscale Engineering for Low-Temperature Ceramic Fuel Cells" 

                                                                                                               Young Beom Kim  


                                                                                                 Department of Mechanical Engineering 
                                                                                                        Advisor:  Prof. Fritz B. Prinz 

                                                                                                       Date:  Friday, May 13th, 2011 
                                                                                             Time: 10:00am (Refreshments at 9:45am) 
                                                                                Location: Mitchell Earth Science (Hartley Conference Room) 
                                                                                       http://campus-map.stanford.edu/index.cfm?ID=04-560  



Solid oxide fuel cells (SOFCs) have been under intense investigation for their high energy conversion efficiency and their use in various practical applications. However, due to the high activation energy of ion transport through the solid electrolyte (ohmic loss) and the sluggish oxygen reduction reaction at the cathode side (activation loss), they have usually been operated at a relatively high temperature range (800-1000oC). This high operating temperature poses serious challenges for widespread applications in terms of compatibility of fuel cell components, seal integrity, and structural and thermal stability.

For this reason, there have been numerous efforts to reduce the operating temperature to the lower regime (300-500oC, LT-SOFC). Unfortunately, lowering the operating temperature causes increase of the losses which previously mentioned. To compensate for the increased ohmic resistance due to slow ionic transport through the YSZ layer at low temperature, we developed thin film techniques such as PLD and ALD to reduce the electrolyte thickness down to less than 100nm range and have succeeded at decreasing ohmic resistance. However, as the operating temperature is reduced, the activation loss, which mainly comes from the electrode polarization process at the cathode, still remains a key challenge.

In this talk, three approaches are presented to improve LT-SOFC performance by reducing the activation loss. The first part is the actual electrochemical reaction site control and maximization. The triple phase boundary (TPB) is known as the actual reaction site for fuel cell charge transfer reaction. Nano-pore structured electrodes, which have stability and controllability, were fabricated to optimize and maximize the actual reaction site for performance enhancement. The second approach is to improve charge transfer reaction by adding a thin cathodic interlayer having superior catalytic activity on oxygen kinetics. Nanoscale yttria-doped ceria (YDC) cathodic interlayer was deposited on YSZ by using pulsed laser deposition (PLD) method and surface grain structure contribution on oxygen kinetics was investigated. The third part of the presentation is three-dimensional (3-D) fuel cell architecture fabrication by developing a new process. Increasing effective surface area is important to increase the power output for energy conversion devices. All these approaches and experimental results provide significant implications in designing the LT-SOFCs to improve the performance by reducing the activation loss.


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Young Beom Kim
Ph.D. Candidate 

Nanoscale Prototyping Laboratory for Energy
Mechanical Engineering
Stanford University
440 Escondido Mall, Bldg.530, Rm. 226
Stanford, CA 94305